A possible solution to the ATMA issue!

[File2ish]

Lower drop rate ( to .3%)
Add Lottery Spawn FATES and have Atmas only drop from those lottery spawn FATEs.
?????
Profit.

Though in all seriousness, I think eventually they will change or add more ways to get Atmas to the system (like when they add the next form in a later patch). I don't really have any suggestions.

Maybe a retainer quick venture could get a random atma you don't have via quick venture (if it's not already possible, seeing how we get random items already).

Edit: With the venture thing. a "quick" venture that takes a week, but guarantees a random atma. That wouldn't feel like progression though.